1. Field of the Invention
The present invention relates to air conditioning apparatus and a method of control. More particularly, the present invention concerns integration of an economizer with the operation of an air conditioning unit including means for modulating the damper regulating air flow through the economizer.
2. Description of the Prior Art
A typical air conditioning system having a vapor compression refrigeration circuit includes various components such as a compressor, condenser, evaporator and expansion device. These components are arranged to transfer heat energy between a fluid in heat transfer relation with the evaporator and a fluid in heat transfer relation with a condenser. To provide cooling to an enclosure heat energy is rejected in an outdoor coil serving as a condenser and heat energy is absorbed at the indoor coil serving as an evaporator. This heat energy is absorbed from the air being supplied to the enclosure such that air at a reduced temperature is provided.
It is known in the air conditioning industry to provide an air conditioning unit which is suitable for being mounted on a roof or otherwise adjacent to the enclosure to be conditioned. This unit is typically divided into an indoor section having an indoor heat exchanger and an outdoor section having an outdoor heat exchanger. An indoor fan is mounted within the indoor section for supplying conditioned air to the enclosure. The indoor fan draws this air both from the enclosure as return air and from the ambient as makeup air. The air entering the indoor section is passed in a heat exchange relation with the indoor heat exchanger wherein either heat energy is absorbed from the air flowing therethrough or heat energy is rejected to said air. Consequently the air being supplied to the enclosure is conditioned within the indoor section of the air conditioning unit.
The outdoor section of the unit is arranged such that heat energy may be transferred between the outdoor heat exchanger and the ambient air flowing therethrough. Typically, an outdoor fan is provided to circulate the air through the outdoor heat exchanger. The compressors of a typical system are located within the outdoor section.
It has been found advantageous to utilize air conditioning systems incorporating economizers. As used herein, the term economizer shall refer to that portion of an air conditioning unit adapted to draw ambient air into the indoor section of the unit for supply to the enclosure. It is desirable to circulate outdoor air to the enclosure when its temperature and humidity is such that cooling of the enclosure may be accomplished without operating the refrigeration circuit of the air conditioning unit or may be accomplished utilizing cool ambient air and simultaneously operating the refrigerant circuit.
Utilization of an economizer requires that sufficient volumes of air be circulated such that air may be drawn into the unit through the economizer and thereafter circulated to the enclosure. A sufficient volume of return air must also be circulated back to the air conditioning unit from the enclosure. Under some conditions, a power exhaust fan, return air fan or discharge opening may be utilized such that the return air from the enclosure is discharged to the ambient. Hence, any cooling effected in this mode of operation is caused by the substitution of cool outdoor ambient air for the existing indoor air. The temperature of the outdoor air, as compared to the temperature of the enclosure, is typically the critical factor involved in determining whether it is more cost effective to effect cooling by circulation of ambient air into the enclosure as opposed to operation of the refrigeration circuit.
The invention as disclosed herein concerns controls for integrating the operation of an economizer and vapor compression refrigeration circuit for supplying cool air to an enclosure in the most cost effective manner. The control circuit further concerns the incorporation of circuits to modulate dampers to provide the correct amount of outdoor air to maintain the appropriate return air temperature to the enclosure.